It is often desirable to non-invasively determine the position or setting of a mechanical device, such as a switch, valve, pressure setting mechanism, or other sensor or control, and to be able to indicate the setting to a remote device.
By way of illustration, treatment of hydrocephalus can involve selecting a pressure setting on an implantable valve to control the flow of cerebrospinal fluid through a hydrocephalus shunt. Hydrocephalus is a neurological condition that is caused by the abnormal accumulation of cerebrospinal fluid (CSF) within the ventricles, or cavities, of the brain. CSF is a clear, colorless fluid that is primarily produced by the choroid plexus and surrounds the brain and spinal cord, aiding in their protection. Hydrocephalus can arise when the normal drainage of CSF in the brain is blocked in some way, which creates an imbalance between the amount of CSF produced by the choroid plexus and the rate at which CSF is absorbed into the bloodstream, thereby increasing pressure on the brain.
Hydrocephalus is most often treated by surgically implanting a shunt system in a patient. The shunt system diverts the flow of CSF from the ventricle to another area of the body where the CSF can be absorbed as part of the circulatory system. Shunt systems come in a variety of models and typically share similar functional components. These components include a ventricular catheter, which is introduced through a burr hole in the skull and implanted in the patient's ventricle, a drainage catheter that carries the CSF to its ultimate drainage site, and optionally a flow-control mechanism, e.g., shunt valve, that regulates the one-way flow of CSF from the ventricle to the drainage site to maintain normal pressure within the ventricles. The shunt valve can have several settings which determine the pressure at which it will allow CSF to flow the ventricular catheter to the drainage catheter. It is this pressure setting, which can correspond to the position of components in the valve, that may need to be determined.
In some cases, determining the pressure setting of a shunt valve can be accomplished using X-rays, magnetic tools, and/or using acoustic feedback. However, it would be advantageous to provide a pressure setting indicator that offers more accurate information directly from the shunt valve, instantaneously and without the need for radiation or cumbersome instruments. Such considerations can apply to a wide range of applications involving settings for implanted or embedded controls, valves, switches, and so on, both in medical devices and elsewhere.
Accordingly, there remains a need for non-invasively indicating the position or setting of a mechanical device, particularly in implanted medical devices.